An electronic engine control arrangement for a motor vehicle is disclosed in the publication entitled "Elektronische Motorsteuerung fur Kraftfahrzeuge", Motortechnische Zeitschrift, 46th year, Volume 4, 1985. A measuring unit configured as a potentiometer transmits the position of an operator-controlled element actuable by the driver to an open-loop/closed-loop control unit. The control unit forms a desired value for a position control of the power-determining element of the engine from the position signal of the operator-controlled element and possibly from further operating variables of the engine and/or the vehicle. A controller compares the desired value formed in this manner to an actual value of the position of the power-determining element or of the electrically actuable positioning motor connected to this power-determining element with the actual value being detected by a further measuring unit. The control output signal actuates the positioning motor in the sense of a control of the desired value to the actual value.
This control takes place during operation of the motor vehicle, that is, when the accelerator pedal is actuated as well as during the idle operating condition of the engine. What is different from the above-described vehicle operation is that in the idle operating condition, the desired value for the position control of the power-determining element is determined in dependence upon operating variables of the engine and/or of the motor vehicle with a view to a pregiven desired engine speed.
Since for this control of the idle engine speed in the idle operating condition of the engine and in contrast to the straight position control, a higher precision is required of the position control and its components, a measuring unit having a very high resolution capacity with respect to the position of the element over its entire range of movement is provided for detecting the position of the power-determining element. Analog components and components of the open-loop/closed-loop control unit having high resolution are connected with the foregoing especially analog-to-digital converters converting the analog position signal into digital values. Components of this kind have a very high resolution over the entire range of movement of the power-determining element or of the actuating element and are, as a rule, complex and expensive as are the analog components.
Furthermore, these measuring units and components must satisfy the strict requirements for utilization in motor vehicles with respect to tolerance, resistance to temperature, sensitivity to contaminants, availability and operational reliability. These factors increase additionally the cost and complexity.